A so-called compact disc (CD), among disc-shaped recording mediums, has many standards, which can be roughly classified into a standard for a compact disc-digital audio (CD-DA) and a compact disc-read-only memory (CD-ROM).
The CD-DA is a standard for audio. On the disc of the CD-DA standard (referred to hereinafter as a CD-DA disc), digital audio data, generated on sampling analog audio signals, are recorded with a so-called constant linear velocity (CLV). Thus, when reproducing audio signals from the CD-DA disc, the latter is run in rotation at a constant linear velocity (CLV) and the digital audio data read out from the disc at a constant reproducing rate is digital/analog converted for regenerating analog audio signals. For the above-mentioned constant linear velocity, the velocity of 1.2 m/s to 1.4 m/s is prescribed.
On the other hand, the CD-ROM, which is the standard for a replay-only memory employing the CD, can store various information items of not less than hundreds of megabyte on one disc. The disc conforming to the CD-ROM standard can store various data such as computer programs, audio data, video data or letter data. Since the data recorded on the CD-ROM disc is reproduced by a computer, the audio data recorded on the CD-ROM is handled similarly to the above-mentioned computer data, video data or letter data.
In the following description, the audio data of the CD-ROM standard is termed CD-DA data, while the data of the CD-ROM standard is termed CD-ROM data, for demarcation therebetween. Although the CD-ROM disc is generally used as a read-only recording medium, there is also such a disc type on which the user can write data. In the CD-DA disc or the CD-ROM disc, the recorded information is managed by a series of domains termed tracks. One to a maximum of 99 tracks can be recorded on a sole disc. Audio data is recorded on these tracks of the CD-DA disc.
It should be noted that the CD-ROM, which is one of the CD standards, is reproduced by a computer as described above, so that, depending on the processing capability of the computer and that of the disc driving device, the CD-ROM disc can be read at a faster rate than the reproducing speed of the CD-DA disc. That is, in a computer employing the CD-ROM disc as an external recording medium, the CD-ROM disc can be rotated at an elevated velocity for retrieving and reading out desired data from the CD-ROM disc, while data can be reproduced in accordance with a random-access system. At this time, the rotational velocity used in reading out CD-ROM data from the CD-ROM disc is significantly faster than that used in reproducing audio data from the CD-DA disc.
Specifically, if the playback speed used in reproducing the CD-DA disc is the standard playback speed (or the usual playback speed), the CD-ROM disc can be reproduced at double the standard playback speed (double-speed reproduction), at four times the standard playback speed (quadrupled-speed reproduction) or at six times the standard playback speed (sextupled-speed reproduction). Recently, octatupled playback speed (eight times the standard playback speed) or the 10-tupled playback speed (ten times the standard playback speed) are making their debut. With the constant linear velocity, the rotational velocity in reproducing the CD-DA disc is approximately 500 rpm and approximately 200 rpm on the inner and outer disc rim sides, respectively. On the other hand, if the CD-ROM disc is reproduced at, for example, the 10-tupled speed, by the constant linear velocity, the rotational velocity in reproducing the disc is approximately 5000 rpm and approximately 2000 rpm on the inner and outer disc rim sides, respectively. In the following description, the playback velocity faster than the double speed is collectively termed multiple-speed reproduction.
An illustrative structure of a disc reproducing device, capable of reproducing the above-mentioned CD-DA disc or a CD-ROM disc, is shown in FIG. 16. The structure of FIG. 16 is that of a CD-ROM drive capable of reproducing a CD-DA disc as well.
In FIG. 16, a disc 110, which is the above-mentioned CD-DA disc or CD-ROM disc, is run in rotation by a spindle motor 121.
An optical pickup 111 converges and illuminates a laser light beam on the disc 110 for reading out signals recorded thereon. The signals read out from the disc 110 by the optical pickup 111 are routed to a RF amplifier 112.
The RF amplifier 112 includes an automatic power control (APC) circuit for automatically controlling the laser power of a laser diode of the optical pickup 111. An output of the RF amplifier 112 is routed to a servo circuit 113.
The servo circuit 113 detects focusing error signals and tracking error signals, based on the output of the RF amplifier 112, and routes these error signals to a biaxial driver 118. This biaxial driver 118 drives a biaxial actuator of the optical pickup 111 based on the focusing error signals and the tracking error signals. This realizes the focusing servo and the tracking servo.
The servo circuit 113 also generates sled control signals for moving the optical pickup 111 to a target radial position of the disc, based on the control from a CPU 123, and sends these sled control signals to a sled driver 119. The sled driver 119, receiving the sled control signals, drives a sled motor of a sled unit, not shown. The optical pickup 111 is moved along a sled rail.
The output of the RF amplifier 112, via the servo circuit 113, is routed to a signal processing circuit 114. Since the signals recorded on the disc 110 are modulated signals modulated by so-called eight-to-fourteen modulation (EFM), the signal processing circuit 114 demodulates the EFM signals. Moreover, since error correction codes by cross interleave Reed-Solomon code (CIRC) is appended to the recorded signals, the signal processing circuit 114 corrects the recorded signal for errors using the error correction code.
If the disc 110 is the CD-DA disc, the signals demodulated and corrected for errors by the signal processing circuit 114 become the above-mentioned CD-DA data which are converted by a digital/analog (D/A) converter 124 into analog audio signals so as to be outputted at an audio output terminal 125.
On the other hand, if the disc 110 is the CD-ROM disc, the signals demodulated and corrected for errors by the signal processing circuit 114 are routed to a CD-ROM decoder 115. Since the CD-ROM data recorded on the disc 110 which is the CD-ROM disc has the error detection and correction codes further appended thereto in accordance with the CD-ROM standards, the CD-ROM decoder 115 detects and corrects the errors, that is decodes the data. The CD-ROM data, decoded by the CD-ROM decoder 115, is routed via an interfacing circuit 116 and an output terminal 117 to, for example, a downstream side host computer.
The signal processing circuit 114, performing the above-described demodulation and error correction, generates a disc rotating speed control signal for performing the CLV control from the signals read out from the disc 110. If the disc 110 is the CD-DA disc, the disc rotating speed control signal is a signal used for rotation-controlling the disc 110 to the above-mentioned standard reproducing velocity, whereas, if the disc 110 is the CD-ROM disc, the disc rotating speed control signal is a signal used for rotation-controlling the disc 110 to the above-mentioned multiple reproducing velocity.
The disc rotating speed control signal is routed to a spindle driver 120 which then generates a driving voltage for driving the spindle motor 121 from the disc rotating speed control signal.
Among the CD standards, there is such a standard in which audio data of the CD-DA standards (CD-DA data) and the CD-ROM data of the CD-ROM standards are recorded in separate areas of the same disc. In the following explanation, this disc is termed a combined disc.
This combined disc has a recording area for recording the CD-ROM data of the CD-ROM standard (referred to hereinafter as a CD-ROM area 202) on the inner disc rim side, whilst a recording area for recording CD-DA data of the CD-DA standard (referred to as a CD-DA area 203) on the outer disc rim side, as shown in FIG. 17. The CD-ROM area 202 and the CD-DA area 203 are provided separately from each other. In the embodiment of FIG. 17, the CD-DA area 203 is provided on the outer disc rim side, whilst the CD-ROM area 202 is provided on the inner disc rim side, these areas 203, 202 making up a program area 205. A lead-in area 201 and a lead-out area 204 are provided on the innermost and outermost areas of the disc, respectively.
The disc reproducing device of FIG. 16 can reproduce a disc 110 which is the above-described combined disc. In this case, the CD-ROM data, reproduced from the CD-ROM area 202, is outputted at the output terminal 117 through a path by which the CD-ROM disc is reproduced. On the other hand, the CD-DA data, reproduced from the CD-DA area 203 of the disc 110, is outputted at an audio output terminal 125 through a path by which the CD-DA disc is reproduced.
Since the data recorded in the CD-ROM area 202 of the disc 110 which is the above-mentioned combined disc is the CD-ROM data, the CD-ROM area 202 can be reproduced by the disc reproducing device by multiple speed reproduction as in the case of reproducing the CD-ROM disc.
However, if the CD-DA area 203 of the combined disc is reproduced by the above disc reproducing device, the reproduction needs to be preformed with the above-mentioned standard reproducing speed, because the data recorded on the CD-DA area 203 is the CD-DA data.
Thus, there is produced a difference in the reproducing speed when reproducing the CD-ROM area 202 and when reproducing the CD-DA area 203. This difference is accentuated especially when the CD-ROM area 202 is reproduced with the quadrupled reproducing speed. If, in the disc reproducing device designed for coping with 10-tupled speed, the combined disc, having the CD-DA area 203 on its outer disc rim side and the CD-ROM area 202 on its inner disc rim side, the rotating speed of the disc is 200 rpm and 5000 rpm on the outer and inner disc rim sides, respectively, if the disc is reproduced with CLV.
For varying the rotating speed of the disc in a range from 200 to 5000 rpm, a significant amount of torque is required of the spindle motor. Thus, with this type of the disc reproducing device, the spindle motor is increased in size to render it difficult to reduce the size of the device. Moreover, with this type of the disc reproducing device, the spindle motor suffers from increased power consumption and concomitantly increased heat evolution. This increased power consumption is not desirable in applying the disc reproducing device to a battery-driven portable terminal.
Moreover, if the CD-ROM area 202 and the CD-DA area 203 are alternately reproduced, this speed difference imposes a significant load on the spindle motor designed for rotating the disc. Specifically, if the CD-ROM area 202 is first reproduced and subsequently the CD-DA area 203 is reproduced, the rotating speed of the disc needs to be dropped at a time from the multiple disc rotating speed to the standard disc rotating speed. Conversely, if the CD-DA area 203 is reproduced and subsequently the CD-ROM area 202 is reproduced, the rotating speed of the disc needs to be increased at a time from the standard disc rotating speed to the double disc rotating speed. This imposes a significant load on the spindle motor resulting in the shortened service life of the disc driving mechanism of the disc reproducing device.
In addition, if the CD-ROM area 202 and the CD-DA area 203 are alternately reproduced, the follow-up time for the rotating speed of the disc to reach one of the above-mentioned reproducing speeds is also required thus leading to delayed accessing. Although the follow-up time can be shortened to speed up the accessing, this shortened follow-up time leads to a further excess load imposed on the spindle motor.
For a spindle motor capable of coping with all of the above requirements, only a limited type of the spindle motor can be used, thus imposing designing limitations.
Also, the disc reproducing device reads out data from a disc responsive to a readout command from the host computer. However, in reproducing the above-mentioned combined disc, it is only one of the readout command for the CD-ROM area 202 and the readout command for the CD-DA area 203 that can accept the readout command from the host computer at a time, while the two commands cannot be accepted simultaneously. That is, if the CD-ROM area 202 and the CD-DA area 203 are reproduced alternately, and one of the readout command for the CD-ROM area 202 and the readout command for the CD-DA area 203 is received, the other of the readout command cannot be accepted nor executed until the received readout command is executed and has come to a close.
In view of the above-described status of the art, it is an object of the present invention to provide a disc reproducing device and method in which, when reproducing data that permits high-speed reproduction, such as CD-ROM data, and data to be inherently reproduced at a standard reproducing speed, such as CD-DA data, both data can be reproduced with short accessing time without unduly loading the spindle motor, in which the service life of the disc drive unit can be extended to reduce the size of the device and to diminish the power consumption and heat evolution, and in which the CD-ROM data and the CD-DA data can be read out in parallel.